A general problem in controllers and controller circuits is the calculation of the steady state time, i.e., the point in time at which the control variable has approached the command variable with sufficient precision. The difference between the command variable and the control variable will be referred to in the following as deviation and the absolute value of the deviation will be referred to as the amount of deviation. The difficulty of calculating the steady state behavior of the controller is present in all controllers in which the deviation decays during the steady state sequence, either due to an oscillation sequence or aperiodically, for example, in a PT (proportional with time constant) controller, in particular a PT controller with a degree greater than one, for example, a PT2 controller in which an insulated oscillation sequence occurs during the steady state phase, but also, for example, in a PDT (proportional and differentiating with time constant) or PIT (proportional and integrating with time constant) controller. The classification of controllers cited above may be found by way of example in G. Schmidt, “Grundlagen der Regelungstechnik” [Fundamentals of Control Engineering], 2nd edition, ISBN 3-540-17112-6, 1989, Table 2.6 on pages 98 and 99.
All controllers that are subjected to an oscillation sequence present the problem that the regulation is not yet fully functional as long as the controller is not yet in a steady state. Solutions to this problem exist in which a sequence that is dependent upon the controller may not be released until the controller is in a steady state. For example, an electronic measuring device has an automatic regulation of the level intensification of the input signal (ALC, automatic level control). This automatic control of the level intensification produces a controller circuit that is subjected to an oscillation sequence. The measuring procedure, for example, a signal vector analysis, may not be initiated until the oscillation sequence is completed. On the other hand, the lag time before the initiation of the measurement should be kept as short as possible in order to reduce the total measuring time of the measuring device and to prevent unnecessary lag time.
In chapter 2.9.6.4 on pages 107 and 108 of the abovementioned book by G. Schmidt, “Grundlagen der Regelungstechnik,” the recommendation is made, in the case of a PT2 controller whose transmission function displays a dampened oscillation during the steady state phase, for the steady state time to be defined such that the envelope of the transmission function has decayed to 5% of the steady-state value (asymptotic limiting value of the transmission function). However, no definitive information regarding the steady state time can be acquired from the definition that the steady state sequence is defined as having ended when the envelope of the transmission function and/or the deviation has decayed to 5% because the steady state time depends on the initiation conditions. The abovementioned book therefore has only a crudely estimated description of steady state time for a PT2 controller as a function of the angular frequency and the damping constant. For many applications, however, this estimate is not sufficiently precise. For example, in the application mentioned at the outset of the automatic level regulation in the framework of a series of measurements for vector analysis, several input signals with different levels are measured and an unnecessary lag time for the steady state of the level of every input signal to be measured would severely increase the measurement time.
There exists therefore a need to provide a method and device for calculating the steady state time of a controller with which the steady state time may be calculated with a high degree of precision.